In the field of surveying, measurement, or BIM (Building Information Molding), a three-dimensional position of a measurement point is measured by generally using a surveying machine for measuring a distance and an angle, and a retroreflection prism. In this measurement, the optical reflecting point of the prism cannot be directly placed on the measurement point because the prism has a specified dimension. Accordingly, the prism is usually fixed to a pointing rod (or a pointing stand).
More in detail, after the front end of the pointing rod is placed on the measurement point, and the prism is fixed at the position deviated by a known fixed distance from the measurement point, the three-dimensional position measurement of the prism is performed while the vertical situation of the pointing rod is secured by using a bubbler tube. Then, the three-dimensional position of the measurement point is calculated by moving the measured value toward the downward direction by the above fixed distance. However, this method is not applicable to a measurement in which the pointing rod is inclined such as for a room corner.
On the other hand, another system of measuring a three-dimensional position is proposed in which the measurement can be conducted if the pointing rod is inclined from the measurement point. For example, in Patent Publication 1, after two reflection prisms are fixed and separated from each other by a known distance on a pointing rod, the two points of the prisms are measured for calculating the position of the measurement point from the two three-dimensional positions. In Patent Publication 2, the position of the measurement point is calculated by using values of an incident angle sensor and an inclination sensor possessed by a pointing rod.